<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button onclick="handle()">请求</button>

    <!-- <script>
        function handle(){
            let xhr = new XMLHttpRequest();
            xhr.open('GET','http://localhost:3000',true)
            xhr.send()
            xhr.onreadystatechanged = function(){ //请求当前状态
                // 0 初始化 状态
                // 1 open 状态
                // 2 send 状态
                // 3 正在解析接受数据
                // 4 完成状态
                if(xhr.readyState == 4 && xhr.status == 200){
                    console.log(xhr.responseText);
                    
            }
        }
    }
    </script> -->

    <script>
        function jsonp(url,cb){
          const script = document.createElement(script)
          window[cd] = function(data){
            console.log(data);    
          }

          script.src = `${url}?cb=${cb}`

          document.body.appendChild(script)
        }

        function handle(){
           jsonp('http://localhost:3000','callback');
        }
    </script>
</body>
</html>